1. Field of the Invention
This invention relates to liquid controlled release nitrogn fertilizers produced from ammonia, urea, and formaldehyde. More particularly, it relates to a new method using high reaction temperature, low reaction basicity, and a high ammonia molecular ratio for preparing aqueous liquid nonpolymeric controlled release nitrogen fertilizer, exhibiting low phytotoxicity because the condensation reaction is substantially complete, leaving almost no unreacted ammonia, urea, and formaldehyde.
2. Description of the Prior Art
Urea formaldehyde condensation polymers have been used for a long time to provide fertilizers which release slowly to feed growing plants. These polymer products when prepared with low free urea contents contain large amounts of high molecular weight polymers which do not release their nitrogen contents in a timely and predictable pattern as needed to safely and efficiently feed plants. Liquid urea formaldehyde products disclosed heretofore in addition to methylene urea polymers also contain substantial amounts of unreacted urea, and ammonia which cause chlorosis and damage to plants fertilized. Damage is particularly severe when nitrogen liquids containing substantial amounts of unreacted urea and ammonia are applied on the foliage of plants.
In the past hexamethylene tetramine, formed by the condensation reaction of formaldehyde and ammonia, containing no urea and little free ammonia, was tried as a nitrogen foliar feed, and was found to exhibit phytotoxicity to the foliage of plants. A condensation reaction is defined as a reaction combining two or more molecules by splitting out water.
In U.S. Pat. No. 4,554,005, Hawkins disclosed a method of preparing a storage stable urea formaldehyde based nitrogen fertilizer solution by reacting urea, formaldehyde, and ammonia in the presence of aqueous caustic in a molecular ratio of between 2 and 1, 1, and between 0.2 and 0.38, at a temperature between 85.degree. and 95.degree. C., for between 55 and 120 minutes in two stages. The composition disclosed by Hawkins contained substantial amounts of s-triazine and unreacted urea.
Moore, in U.S. Pat. No. 4,781,749, disclosed the preparation of storage stable aqueous liquid polymethylene urea by reaction of urea, formaldehyde, and ammonia in a molecular ratio of between 1.3 and 1.5, 1, and between 0.25 and 0.30 in a two stage method carried out at near boiling temperatures with sufficient buffering agent to maintain near neutral conditions. The liquid product contained primarily water soluble polymethylene ureas, unreacted urea, methylolurea, methylene diurea, and unreacted ammonia.
Thomas P. Murray disclosed the isolation of 5-methyleneuriedo-2-oxohexahydro-s-triazine, a nonpolymeric condensed urea, ammonia, formaldehyde reaction product in liquid controlled release nitrogen fertilizers. He also provided a high performance liquid chromatography (HPLC) analytical method for its quantitative analysis. Products analyzed by Murray contained between 19 and 31 percent of the aforementioned compound and substantial amounts of unreacted urea.
It has long been a goal in the art to produce a storage stable, controlled releasing liquid fertilizer and foliar feed with complete nitrogen availability and a low degree of phytotoxicity. To achieve these goals, it is necessary to prepare a liquid wherein the ammonia, urea, and formaldehyde are substantially condensed into a nonpolymeric water soluble liquid substantially free of unreacted ammonia, urea, and formaldehyde.